A steering lock device is disclosed in Patent Literature 1. As illustrated in FIG. 1, this steering lock device 101 includes, inside a frame 102 and a frame cover 103, a lock bolt 105 capable of moving between a lock position in which the lock bolt is engaged with a steering shaft (not illustrated) and an unlock position in which the engagement is released, and an auxiliary lock structure 106 configured to prevent movement of the lock bolt 105 in the lock position. The auxiliary lock structure 106 includes: an auxiliary lock member 161 biased by the biasing force of a coil spring 162 from a disengagement position in which the auxiliary lock member 161 is not engaged with the lock bolt 105 in the lock position toward an engagement position in which the auxiliary lock member 161 is engaged with the lock bolt 105; a stopper member 131 engaged with the auxiliary lock member 161 to thereby hold the auxiliary lock member 161 in the disengagement position; and a holding member 131a engaged with the stopper member 131 to thereby hold the stopper member 131 in a prevention position. The stopper member 131 is arranged in such a way as to be movable between the prevention position in which the stopper member 131 is engaged with the auxiliary lock member 161 and an open position in which the engagement is released. The holding member 131a is mounted in such a way as to be capable of falling to the inner surface of the frame 102 or the frame cover 103.
With the holding member 131a mounted in such a way as to be capable of falling to the inner surface of the frame 102 or the frame cover 103, the holding member 131a, upon an improper unlocking action such as a destructive action from outside, falls from the frame cover 103 and thus releases the hold of the stopper member 131, so that the stopper member 131 and the auxiliary lock member 161 are actuated. In this way, even if part of the frame 102 or the frame cover 103 is destroyed, the lock bolt 105 can still be held in the lock position. Thus, antitheft security is improved.